Feb 6 (Reuters) - Utility crews on Thursday worked to restore power to hundreds of thousands of homes and businesses in the U.S. Northeast after a snow and ice storm slammed the region. But flights began returning to normal after thousands of delays or cancellations.

The latest in a series of winter blasts dumped up to about a foot (30 cm) of snow on Wednesday and early Thursday on the Eastern Seaboard from Maryland to Maine. About 100 million people - or one-third of the U.S. population, lives in the region.

The storm coated roads with ice and broke tree limbs, knocking down power lines. At least four deaths were related to the storm, authorities said.

Pennsylvania was the hardest hit. At one point, 849,000 customers were without power, according to the Pennsylvania Emergency Management Agency. By 8 a.m. EST (1300 GMT), utility crews had gotten number down to just over 500,000, the agency said.

"The storm that we had yesterday is pretty much done for Pennsylvania," said Craig Evanego, a forecaster with the National Weather Service in State College, Pennsylvania.

Airports began clearing backlogs, with 479 flights throughout the United States canceled as of 10 a.m. EST (1500 GMT), down from 2,893 flights on Wednesday, according to FlightAware.com, an online flight tracking site.

Snow continued falling in patches along the East Coast, but by early on Thursday the storm appeared to have largely run its course, the National Weather Service said.

The East was not the only area hit by snow. In Dallas, an early morning dusting snarled morning traffic.

In Baltimore, pawnshop worker Sheila Bateman said her morning jog with her dogs has become a slippery romp.

"I would be better off with ice skates than running shoes. The dogs sometimes go sliding with their legs going out from under them," she said.

The storms have taken their toll on the region, slowing construction, putting a damper on shopping and depleting stocks of the salt used to keep roads ice-free in some areas.

New Jersey, for example, had spent $60 million on snow removal as of Jan. 26, putting it on track to break the record of $62.5 million spent last year, said Joe Dee, a spokesman for the state Department of Transportation.

Most states and major cities do not try to set an upper limit on spending for snow removal but authorize agencies to spend what is necessary and count on legislatures to cover the cost.

A lot of the salt in the Chicago area is delivered along the Mississippi and Illinois rivers on barges, but the Illinois was frozen on Thursday. The salt was arriving by truck, increasing costs, said Tom Breier, general manager of Ice Melt Chicago, a supplier based in Lisle, Illinois.

The winter siege, which by now seems never-ending for some, could produce yet another barrage of bad weather, according to the National Weather Service's Evanego.

"It looks like this weekend there could be a system that comes through and there could be some (more) snow," he said. (Writing by Jon Herskovitz; Additional reporting by Mary Wisniewski in Chicago, Edward Krudy and Scott DiSavino in New York, Richard Weizel in Connecticut,)